Certain secondary combustion chambers for stationary gas turbines, the temperature of the entering working gas is above the self-ignition temperature for the gaseous or liquid fuel. These combustion chambers are typically configured for premixing combustion with a low content of pollutants and have internal fittings which cause a wake in the gas flow giving rise to the risk of undesirable flame retention.
Fuel injectors, as an example of a component integrated in a gas-turbine combustion chamber, are often formed with a curved feed part exposed to the combustion-chamber flow. The fuel-nozzle holder which is disposed transversely to the main flow forms a wake region with recirculating flow just like the blunt end of the nozzle itself. At this location, that is, in the wake region behind the transversely disposed part of the lance-like fuel injector, an inadequately mixed fuel/air mixture can be transported upstream by the locally recirculating flow behavior. Consequently, instead of a premixing flame, a diffusion flame having higher pollutant production then appears in the wake. The flame burns in a stable manner in this wake region, since fuel is constantly transported by the flow recirculation from the injection point into the wake region.
The disadvantage of this prior art is that pollutant formation, compared with the intended premixing combustion downstream of the fuel injector, is usually clearly increased in such a flame due to the relatively long retention times in the combustion zone and the high flame temperature. This effect is undesirable in view of the progressively stricter requirements imposed on pollutant emission.
The thermal loading of the component (e.g. the fuel injector) can likewise increase and thus necessitate more expensive cooling of the component wall.